New here! 50cc build

[Karl Snarl]

I build a lot of pocket bike engines, squish is over 0.060" stock and I have taken them down to 0.035". That mod alone makes great power over stock.
This is my first bicycle engine, hoping to learn a lot. What is stock squish and how far have you guys gone with the squish?

I know these start around 6:1 which I consider low but seems to be just fine. I obviously haven't finished the motor yet. This winter as I have been cleaning up the intake and exhaust ports, I might widen the exhaust port as well.

Now, this is a budget build, $150 with bicycle, I am at $135, just wanted a few free mods to run a few buddies bikes. One will have a 66/80. Eventually I will build a 66/80 just so you know.
Thanks in advance.

I keep my squish about .8-.7mm. these engines are to sloppy to risk anymore, at least in my head. Go over 9:1 on compression and you'll need to start upping octane or retarding timing or both. 9:1 is about as far as you really want to take it if you are expecting longevity. Gudgeon bearing really takes a beating when you start getting up there in compression.

 

[Atvrunner2]

Good to know, thank you. I know it is said to run 87, I would have no problem running 95 octane or more. This is not a commuter bike. But definitely wanted to know the limits, which I may eventually push it and the rebuild it. For now I will probably go with your suggestion around that .7-.8mm.
Has anyone tried to taper bore the stock carburetor? Unfortunately I have the 'speed' one, but I will buy an NT one a bit later. Was just thinking to try that since it works well on every other 2 stroke I have done. Then a better pipe. See what that nets in power.
Typically in the case reed PB motors the 40mm stays cooler with the extra cylinder meat, over the 44mm engines. Not sure if that is the case with these bicycle engines.

 

[DieselTech]

I think a aftermarket racing cylinder head with the oversized cooling fins goes along ways on these engines in keeping them cool & making a little power to boot.

 

[Atvrunner2]

True, that might have to be my route, assuming the bolt pattern is the same. I never researched or checked that. The dome is probably way better.

 

[DieselTech]

True, that might have to be my route, assuming the bolt pattern is the same. I never researched or checked that. The dome is probably way better.

Bolt pattern on the 49cc & 66cc are the same I believe. Biggest thing to watch for is that the head is cut for your cylinder bore diameter.

 

[Street Ryderz]

Good to know, thank you. I know it is said to run 87, I would have no problem running 95 octane or more. This is not a commuter bike. But definitely wanted to know the limits, which I may eventually push it and the rebuild it. For now I will probably go with your suggestion around that .7-.8mm.
Has anyone tried to taper bore the stock carburetor? Unfortunately I have the 'speed' one, but I will buy an NT one a bit later. Was just thinking to try that since it works well on every other 2 stroke I have done. Then a better pipe. See what that nets in power.
Typically in the case reed PB motors the 40mm stays cooler with the extra cylinder meat, over the 44mm engines. Not sure if that is the case with these bicycle engines.

The speed carb is just slightly bigger I.D. through the body than the regular NT carb but other than that they are identical.

 

[Street Ryderz]

Bolt pattern on the 49cc & 66cc are the same I believe. Biggest thing to watch for is that the head is cut for your cylinder bore diameter.

The bcd for the 48cc being a 40mm bore is not the same and there are no aftermarket cnc heads for it, there used to be a pancake style head but few still sell it, though most 50cc scooter heads are adaptable.

 

[DieselTech]

The bcd for the 48cc being a 40mm bore is not the same and there are no aftermarket cnc heads for it, there used to be a pancake style head but few still sell it, though most 50cc scooter heads are adaptable.

Thanks StreetRyderz I wasnt aware the 48cc were different bolt pattern, I knew they were a 40mm bore, & figured the 66/80cc was based off of it. Thanks I learned something new. Thanks for correcting me. I try not to advise in what I dont know as I'm learning as well.

 

[Greg58]

I run two 48cc bikes, the only head I have found with a squish band is the grubee gt2b head, my avatar bike engine is from bgf on ebay. That engine came with a head without the squish band. Stock 25 mph was all the grubee would do, the bgf engine was a turd, about 20-21 was all it had. After widening the ports and all the other things learned here and the other forum I get 32mph from both. The grubee engine is the fastest, it's in a 24" tire bike, I did much more to it tho, both are over 10 years old.

 

[Greg58]

I have a 66cc bike as well but enjoy the 48 much better, mine are so smooth and a joy to ride.